SwiftUI show loading view while core data is being loaded - core-data

Question

How I can show loading view while core data is being loaded?.
Currently my app's core data store some many images in Binary Data. So when I switch to another tab showing data stored in core data, app lags 1.5 seconds.
So here are two things I have tried:
first I tried to minimize amount of data being loaded from core data using downsample function:
func downsample(imageAt imageURL: Data, to pointSize: CGSize, scale: CGFloat = UIScreen.main.scale) -> UIImage? {
// Create an CGImageSource that represent an image
//CGImageSourceCreateWithData(_ data: CFData, _ options: CFDictionary?)
let imageSourceOptions = [kCGImageSourceShouldCache: false] as CFDictionary
guard let imageSource = CGImageSourceCreateWithData(imageURL as CFData, imageSourceOptions) else {
return nil
}
// Calculate the desired dimension
let maxDimensionInPixels = max(pointSize.width, pointSize.height) * scale
// Perform downsampling
let downsampleOptions = [
kCGImageSourceCreateThumbnailFromImageAlways: true,
kCGImageSourceShouldCacheImmediately: true,
kCGImageSourceCreateThumbnailWithTransform: true,
kCGImageSourceThumbnailMaxPixelSize: maxDimensionInPixels
] as CFDictionary
guard let downsampledImage = CGImageSourceCreateThumbnailAtIndex(imageSource, 0, downsampleOptions) else {
return nil
}
// Return the downsampled image as UIImage
return UIImage(cgImage: downsampledImage)
}
let small = downsample(imageAt: data, to: size)
Image(uiImage: small!)
But there were no difference in lagging time.
So i tried this:
struct ContentView: View {
#Environment(\.managedObjectContext) private var viewContext
#FetchRequest(sortDescriptors: [NSSortDescriptor(keyPath: \ToDoItem2.createdAt, ascending: false)])
var toDoItems: FetchedResults<ToDoItem>
var body: some View {
VStack{
if toDoItems.isEmpty {
LoadingView()
} else {
List {
ForEach(toDoItems) { item in
ToDoItemView(item: item)
}
}
}
}
}
}
Tried to detect no loaded state as toDoItems.isEmpty but it doesn't work
Would be there anyway to show loading view while core data is being loaded?
Thanks

Answer 1

you could try using NSAsynchronousFetchRequest, something like this approach (does not have to be exactly like this (untested) code):
struct ContentView: View {
#Environment(\.managedObjectContext) private var viewContext
#State private var toDoItems: [ToDoItem] = []
#State var isLoading = true
var body: some View {
VStack {
if isLoading {
LoadingView()
} else {
List {
ForEach(toDoItems) { item in
ToDoItemView(item: item)
}
}
}
}
.onAppear {
isLoading = true
let fetchRequest: NSFetchRequest<ToDoItem> = ToDoItem.fetchRequest()
fetchRequest.sortDescriptors = [NSSortDescriptor(keyPath: \ToDoItem.createdAt, ascending: false)]
let asyncFetchRequest = NSAsynchronousFetchRequest(fetchRequest: fetchRequest) { fetchResult -> Void in
if let resutls = fetchResult.finalResult {
self.toDoItems = resutls
}
self.isLoading = false
}
do {
_ = try viewContext.execute(asyncFetchRequest)
} catch {
print("error: \(error)")
}
}
}
}